1. Field of Invention
The invention relates to a sheet feeder, for use in an image forming apparatus, such as a copying machine, a printer, and a facsimile machine, that feeds a sheet of paper with a pick-up roller. More particularly, it relates to such a sheet feeder that restricts excessive rotating force to be transmitted to the pick-up roller from a drive unit, to prevent the pick-up roller and the drive unit from being damaged or malfunctioning.
2. Description of Related Art
A sheet feeder for use in, for example, a facsimile machine is structured so as to feed a stack of recording sheets, one by one, in a predetermined feeding direction by contacting a pick-up roller to upper surfaces of the recording sheets and rotating the roller in a recording sheet feeding direction. Such a sheet feeder typically includes the pick-up roller that provides some frictional force with a surface thereof and that feeds the recording sheets, a motor that generates rotating force, and a plurality of gears that transmit the rotating force of the motor to the pick-up roller. In the sheet feeder, the rotating force of the motor is transmitted to the pick-up roller by the plurality of gears. By the transmission of the rotating force, the pick-up roller contacting the recording sheet is rotated in the recording sheet feeding direction. The pick-up roller separates the topmost recording sheet from a stack of other recording sheets and feeds the topmost recording sheet.
The above-described sheet feeder has some problems in the recording sheet feeding. The motor and the pick-up roller are always connected through the plurality of gears. Therefore, the rotation of the pick-up roller may be restricted due to, for example, paper jams, or even when rotating resistances of the pick-up roller increase, the rotating force of the motor may continuously be transmitted to the pick-up roller and the gears. Therefore, the excessive rotating load is applied to the pick-up roller and the gears, resulting in damage to the pick-up roller and the gears. As the motor is restricted in its rotation, the motor does not operate in accordance with drive pulse signals, and may generate acoustic noise attributable to the repeated rotation in a forward and reverse directions or a further malfunction.